HomeMy WebLinkAboutCT 15-09; QUARRY CREEK PA R-4 EAST; INTERIM REPORT OF TESTING & OBSERVATION DURING SITE GRADING; 2016-10-16Ct I -Ot
INTERIM REPORT OF TESTING
AND OBSERVATION SERVICES
PERFORMED DURING SITE GRADING
QUARRY CREEK
R-4 EAST (LOTS 20 AND 21)
CARLSBAD, CALIFORNIA
PREPARED FOR
CORNERSTONE COMMUNITIES
SAN DIEGO, CALIFORNIA
OCTOBER 10, 2016
PROJECT NO. 07135-42-05
GEOCON
INCORPORATED
GEOTECHNICAL • ENVIRONMENTAL. M A I E R I A L S
Project No. 07135-42-05
October 10, 2016
Cornerstone Communities
4365 Executive Drive, Suite 600
San Diego, California 92121
Attention: Mr. Jack Robson
Subject: INTERIM REPORT OF TESTING AND OBSERVATION
SERVICES PERFORMED DURING SITE GRADING
QUARRY CREEK R-4 EAST (LOTS 20 AND 21)
CARLSBAD, CALIFORNIA
Dear Mr. Robson:
In accordance with your request, we have performed compaction testing and observation services
during grading for Quarry Creek R-4 East. We performed our services during the period of July 7,
2015 through September 29, 2016. The fine grading operation is still in progress. A final report will
be submitted upon completion of grading. The scope of our services included the following:
Observing the grading operation, including removal of undocumented fill, colluvium,
alluvium, and processing the upper surface of the terrace deposits and the placement of
compacted fill.
Performing in-place density tests in fill placed and compacted at the site.
Performing laboratory tests to aid in evaluating compaction characteristics of various soil
conditions encountered. We also performed laboratory. testing on soil samples collected
during grading activities and near finish grade to evaluate expansion characteristics, and
where applicable, water-soluble sulfate content.
Preparing an as-graded geologic map.
Preparing this interim report of grading.
The purpose of this report is to document that the grading of subject project has been performed in
substantial conformance with the recommendations of the project update geotechnical report.
6960 Flanders Dri',e • San Diego, California 92121-2974 0 Telephone 858.558.6900 0 Fax 858.558.6159
GENERAL
Quarry Creek site is located south of State Route 78 and west of College Boulevard in the city of
Carlsbad, California. Areas R-4 is located within the southwestern portion of the overall Quarry
Creek development (see Vicinity Map, Figure 1). Area R-4 East consists of 57 lots designated for
high density, muli-family residential units.
LB3 Enterprises Incorporated performed the grading. Project Design Consultants prepared the
grading plans titled Mass Grading Plans for Quarry Creek, HDP 11-04, Drawing No. 484-5A,
Carlsbad California, with a City of Carlsbad approval date of June 4, 2015. The grading plans
showed sheet-graded pads for R-4. The current grading was performed in accordance with the plans
prepared by SB&O, Incorporated titled Rough Grading Plans for Quarry Creek Planning Area R-4,
dated August 12, 2015 with latest revision dated July 25, 2016. Geocon Incorporated prepared the
project geotechnical report titled Update Geotechnical Investigation, Quarry Creek,
Carlsbad/Oceanside, California, prepared by Geocon Incorporated, dated February 24, 2015 (Project
No. 07135-42-05) and Addendum to Update Geotechnical Investigation, Quarry Creek,
Carlsbad/Oceanside, California, dated March 17, 2015. The following are additional geotechnical
reports pertinent to the project:
Final Report of Testing and Observation Services During Site Grading, Quarry Creek,
Carlsbad, California, prepared by Geocon Incorporated, dated April 4, 2013 (Project
No. 07135-42-02).
Update Report, Quarry Creek R-4, Carlsbad California, prepared by Geocon Incorporated,
dated July 10, 2015 (Project No. 07135-42-05).
We used an AutoCAD file of the grading plans provided by SB&O as the base map to present as-
graded geology and the approximate locations of in-place density tests (Figure 2, map pocket). The
map depicts slopes, building pads, streets and, current and previous ground topography.
References to elevations and locations herein are based on surveyors' or grade checkers' stakes in the
field, elevation shots taken with a Global Positioning System (GPS) unit by the grading contractor,
and/or interpolation from the referenced grading plan. Geocon Incorporated does not provide
surveying services and, therefore, expresses no opinion regarding the accuracy of the as-graded
elevations or surface geometry with respect to the approved grading plans or proper surface drainage.
GRADING
Previous Grading
Portions of the Quarry Creek property have undergone many years of mining, crushing, and screening
to produce commercial aggregate products. The majority of previous mining activity occurred in the
/
Project No. 07135-42-05 -2 -. October 10, 2016
eastern and southern portions of the overall Quarry Creek site. Mining resulted in undocumented fills
and some compacted fill across the former mined areas.
Reclamation grading of the previously mined area commenced in July 2011 and was completed in
December 2012. During reclamation grading, undocumented fills were removed and replaced as
compacted fill. Drop structures, levees, and rock revetment slopes were constructed along and in
Buena Vista Creek drainage. Reclamation grading resulted in removal of undocumented fill and
replacement with compacted fill on the south side of Buena Vista Creek and majority of the areas
north of the creek. Reclamation grading resulted in large sheet-graded pads. The eastern portion of
the site was a part of the reclamation process. The western portion however, was not developed and
consisted of rolling hills and tributary canyons. A summary of observations and compaction tests
performed during reclamation grading is contained in our April 2013 as-graded report.
Recent Grading
Grading within the western portion of the site began with removal of trash, brush, and vegetation
from areas to be graded. The brush and deleterious materials were then exported from the site. Within
areas of planned grading, surficial deposits (i.e., undocumented fill, topsoil, and alluvium) were
removed to competent Terrace Deposits and the Santiago Formation. The surface of existing
compacted fill and the formational materials was scarified, moisture conditioned, and recompacted
prior to receiving additional fill. Fill soils were then placed and compacted in layers until design
elevations were attained. Fills were placed in lifts no thicker than would allow for adequate bonding
and compaction. Grading generally resulted in an approximately three foot-thick soil cap that
generally consist of very low to medium expansive materials. In general, fill materials placed during
grading consist of clayey to silty sand.
A buttress fill was constructed for the north-facing slope along the southern margin of the property.
The purpose of the buttress fill was to intercept a bedding plane shear zone that was 'encountered near
the toe of the slope. The shear key was approximately 30 feet wide and approximately 3 feet below
the bedding plane shear. A heal drain with associated panel drains where installed before backfilling
the buttress.
During the grading operations, oversized rock (material > 6 inches) was placed at least three feet
below design finish grade in graded areas. Rock greater than 12 inches exist within the compacted fill
material placed during previous phases of grading. Oversize rock was spread out within the
compacted fill areas such that soil around the oversize rock could be compacted by the grading
equipment. Although particular attention was given to restricting oversize material placement to the
criteria described above, some oversize chunks could be present in the upper portions of the fill areas.
Project No. 07135-42-05 -3- October 10, 2016
In several los within the south central portion of the site, highly expansive clayey materials were
exposed at finish grade. This material was undercut and replaced with less expansive soils. The clay
was placed in the deeper portion of the fill.
During the grading operation, we observed compaction procedures and performed in-place density
tests to evaluate the dry density and moisture content of the fill material. We performed in-place
density tests in general conformance with ASTM D 6938, Standard Test Methodfor In-Place Density
and Moisture Content of Soil and Soil-Aggregate by Nuclear Methods. A summary of in-place
density and moisture content tests are presented on Table I. Other units within the Quarry Creek
development were graded concurrently with R4. Therefore, the field density tests shown on Table I
are not in sequential order.
Where fill soil contained rock larger than 3/4-inch, a correction was made to the laboratory maximum
dry density and optimum moisture content using methods suggested by AASHTO 1224. The values
of maximum dry density and optimum moisture content presented on Table I reflect these
corrections.
In general, in-place density test results indicate fill soils have a dry density of at least 90 percent of
the laboratory maximum dry density at or slightly above optimum moisture content at the locations
tested. The approximate locations of in-place density tests taken during grading specific to R-4 East
are shown on Figure 2.
We performed laboratory tests on samples of soil used for fill to evaluate moisture-density
relationships, optimum moisture content, and maximum dry density (ASTM D 1557), and shear
strength characteristics (AASHTO T-236). Additionally, we performed laboratory tests on soil
samples collected at various stages of grading and near finish grade (soil fill cap) to evaluate
expansion potential (ASTM D 4829) and where applicable, water-soluble sulfate content (California
Test No. 417). Results of the laboratory tests are summarized on Tables II through IV.
Slopes
Cut and Fill slopes constructed during grading have an approximate inclination of 2:1
(horizontal:vertical) or flatter, with maximum height of approximately 40 feet or less. A. buttress fill
was constructed for stabilizing the north-facing slope along the southern margin of the project site on
the south side of Marron Road. The shear key for the buttress is approximately 30 feet wide and
constructed 3 to 5 feet below the lowest bedding plane shear zone. A heel drain with associated
drainage panels were installed in the backside of the shear key excavation. Documentation of the
buttress fill will be provided in the final as-graded report for R-4.
Project No. 07135-42-05 -4- October 10, 2016
The outer approximately 15 feet of fill slopes were constructed with granular soil and were either
over-filled and cut back or were track-walked with a bulldozer during grading in substantial
conformance with the recommendations of the project geotechnical report. The project slopes have a
calculated factor of safety of at least 1.5 under static conditions with respect to both deep-seated
failure and shallow sloughing conditions.
All slopes should be planted, drained, and maintained to reduce erosion. Slope irrigation should be
kept to a minimum to just support the vegetative cover. Surface drainage should not be allowed to
flow over the tops of slopes.
Finish Grade Soil Conditions
Laboratory test results and field observations indicate that the prevailing soil conditions within the
upper approximately three feet of finish grade. have an expansion potential (El) of 90 or less and
considered as low expansive as defined by ASTM D 4829. These soils are classified as expansive
(El >20) as defined by 2013 California Building Code (CBC) Section 1803.5.3. Table 1 presents soil
classifications based on the expansion index per ASTM D 4829 and the CBC. Table III presents a
summary of expansion index test results for the prevailing subgrade soils at Quarry Creek, Area R-4
Lots 21 and 22.
TABLE I
SOIL CLASSIFICATION BASED ON EXPANSION INDEX
ASTM D 4829
Expansion Index (El) ASTM
Expansion Classification
CBC
Expansion Classification
0-20 Very Low Non-Expansive
21-50 Low
Expansive
Very High
51-90 Medium
91-130 High
Greater Than 130
We performed laboratory water-soluble sulfate testing on samples obtained for expansion testing to
assess whether the soil contains sulfate concentrations high enough to damage normal Portland
cement concrete. Results from the laboratory water-soluble sulfate content tests are presented in
Table IV and indicate that the on-site materials at the locations tested possess "Not Applicable"
sulfate exposure and "SO" sulfate exposure class to concrete structures as defined by 2013 CBC
Section 1904 and ACT 318-08 Sections 4.2 and 4.3. Table 2 presents a summary of concrete
requirements set forth by 2013 CBC Section 1904 and AC! 318. The presence of water-soluble
sulfates is not a visually discernible characteristic; therefore, other soil samples from the site could
Project No. 07135-42-05 -5- October 10, 2016
yield different concentrations. Additionally, over time landscaping activities (i.e., addition of
fertilizers and other soil nutrients) may affect the concentration.
TABLE 2
REQUIREMENTS FOR CONCRETE EXPOSED TO
SULFATE-CONTAINING SOLUTIONS
Water-Soluble MaximumMinimum Sulfate Exposure Sulfate Percent Cement Type Water to Compressive Exposure Class by Weight Cement Ratio Strength (psi) by Weight
Not
Applicable
SO 0.00-0.10 -- -- 2,500
Moderate Si 0.10-0.20 II 0.50 4,000
Severe S2 0.20-2.00 V 0.45 4,500
Very Severe S3 > 2.00 V+Pozzolan or Slag 0.45 4,500
Geocon Incorporated does not practice in the field of corrosion engineering. Therefore, if
improvements that could be susceptible to corrosion are planned, further evaluation by a corrosion
engineer should be performed.
SOIL AND GEOLOGIC CONDITIONS
In general, the soil and geologic conditions encountered during grading were found to be similar to
those described in the referenced project geotechnical report. Lots 21 and 22 of R-4 are underlain by
compacted fill soils (Qcf) overlying Terrace Deposits (Qt).
The as-graded geologic map (Figure 2) has been annotated to show a general representation of the as-
graded geologic conditions observed during grading. Geologic contacts should be considered
approximate.
CONCLUSIONS AND RECOMMENDATIONS
1.0 General
1.1 Based on observations and test results, it is the opinion of Geocon Incorporated that
grading, which is the subject of this report, has been performed in substantial conformance
with the recommendations of the referenced project geotechnical reports. Soil and geologic
conditions encountered during grading that differ from those anticipated by the project
geotechnical reports are not uncommon. Where such conditions required a significant
modification to the recommendations of the project geotechnical reports, they have been
described herein.
Project No. 0713 5-42-05 -6- October 10, 2016
1.2 No soil or geologic conditions were observed during grading that would preclude the
continued development of the property as planned. Based on laboratory test results and
field observations, it is our opinion that the fill soils placed during grading have been
compacted to at least 90 percent relative compaction.
1.3 References to fill thickness or capping of pads are approximate and may be affected by
subsequent fine grading to achieve proper surface drainage.
2.0 Future Grading
2.1 Any additional grading performed at the site should be accomplished in conjunction with
our observation and compaction testing services. Geocon Incorporated should review
grading plans for any future grading prior to finalizing. All trench and wall backfill should
be compacted to a dry density of at least 90 percent of the laboratory maximum dry density
near or to slightly above optimum moisture content. This office should be notified at least
48 hours prior to commencing additional grading or backfill operations.
3.0 Seismic Design Criteria
3.1 We used the computer program US. Seismic Design Maps, provided by the USGS.
Table 3.1 summarizes site-specific seismic design criteria inclOding spectral response
accelerations in accordance with 2013 California Building Code (CBC; Based on the 2012
International Building Code [IBC] and ASCE 7-10), Chapter 16 Structural Design,
Section 1613 Earthquake Loads. The short spectral response uses a period of 0.2 second.
We evaluated the Site Class based on the discussion in Section 1613.3.2 of the 2013 CBC
and Table 20.3-1 of ASCE 7-10. The values presented in Table 3.1 are for the risk-targeted
maximum considered earthquake (MCER). The site is characterized as Site Class D.
Project No. 0713542-05 -7- October 10, 2016
TABLE 3.1
2013 CBC SEISMIC DESIGN PARAMETERS
Parameter Value 2013 CBC Reference
Site Class D Table 1613.3.2
Spectral Response - Class B (0.2 sec), 5s 1.067 g Figure 1613..3.1(1)
Spectral Response — Class B (1 see), S1 0.413 g Figure 1613:3.1(2)
Site Coefficient, Fa 1.073 Table 1613.3.3(1)
Site Coefficient, F 1.587 Table 1613.3.3(2)
Maximum Considered Earthquake 1145 g Section 1613 3.3
Spectral Response Acceleration (0.2 see), 5MS (Eqn 16-37)
Maximum Considered Earthquake 0.656 g Section 1613.3.3
Spectral Response Acceleration (1 see), 5M1 (Eqn 16-38)
5% Damped Design 0 763 g Section 1613.3.4
Spectral Response Acceleration (0.2 see), SDS (Eqn 16-39)
5% Damped Design 0.437 g Section 1613.3.4
Spectral Response Acceleration (1 see), 5D1 (Eqn 16-40)
3.2 Table 3.2 presents additional seismic design parameters for projects located in Seismic
Design Categories D through F in accordance with ASCE 7-10 for the mapped maximum
considered geometric mean (MCEG).
TABLE 3.2
2013 CBC SEISMIC DESIGN PARAMETERS
Parameter Value ASCE 7-10 Reference
Mapped MCEG
Peak Ground Acceleration, PGA 0.407 g Figure 22-7
Site Coefficient, FPGA 1.093 Table 11.8-1
Site Class Modified MCE0
Peak Ground Acceleration, PGAM 0.445 g Section 11.8.3 (Eqn 11.8-1)
3.3 Conformance to the criteria presented in Tables 3.1 and 3.2 for seismic design does not
constitute any guarantee or assurance that significant structural damage or ground failure
will not occur in the event of a maximum level earthquake. The primary goal of seismic
design is to protect life and not to avoid all damage, since such design may be
economically prohibitive.
Project No. 07135-42-05 - 8 - October 10, 2016
4.0 Foundation and Concrete Slab-On-Grade Recommendations
4.1 The foundation recommendations that follow are for one- to three-story residential
structures and are separated into categories dependent on the thickness and geometry of the
underlying fill soils as well as the expansion index of the prevailing subgrade soils of a
particular building pad (or lot). Table V presents the as-graded lot conditions and
recommended foundation categories for Quarry Creek R-4. Determination of fill thickness
and geometry was based on interpretation of field conditions and review of the project
grading plan.
TABLE 4.1
FOUNDATION CATEGORY CRITERIA
Foundation
Category
Maximum Fill
Thickness, T (feet)
Differential Fill
Thickness, D (feet)
Expansion
Index (El)
I T<20 -- EI<50
II 20<T<50 10<D<20 50<EI<90
III 1>50 D>20 90<EI<130
4.2 Table 4.2 presents minimum foundation and interior concrete slab design criteria for
conventional foundation systems.
TABLE 4.2
CONVENTIONAL FOUNDATION RECOMMENDATIONS BY CATEGORY
Foundation Minimum Footing
Embedment Depth Continuous Footing Interior Slab
Category (inches) Reinforcement Reinforcement
I 12 Two No. 4 bars, 6x6-10/10 welded wire
one top and one bottom mesh at slab mid-point
II 18 Four No. 4 bars, No. 3 bars at 24 inches
two top and two bottom on center, both directions
III 24 Four No. 5 bars, No. 3 bars at 18 inches
two top and two bottom on center, both directions
4.3 The embedment depths presented in Table 4.2 should be measured from the lowest
adjacent pad grade for both interior and exterior footings. The conventional foundations
should have a minimum width of 12 inches and 24 inches for continuous and isolated
footings, respectively. Figure 3 presents a wall/column footing dimension detail.
Project No. 07135-42-05 -9- October 10, 2016
4.4 The concrete slab-on-grade should be a minimum of 4 inches thick for Foundation
Categories I and II and 5 inches thick for Foundation Category III.
4.5 Slabs that may receive moisture-sensitive floor coverings or may be used to store moisture-
sensitive materials should be underlain by a vapor retarder. The vapor retarder design should
be consistent with the guidelines presented in the American Concrete Institute's (AC!) Guide
for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials (ACT 302.2R-06). In
addition, the membrane should be installed in accordance with manufacturer's
recommendations and ASTM requirements, and in a manner that prevents puncture. The
project architect or developer should specify the vapor retarder based on the type of floor
covering that will be installed and if the structure will possess a humidity controlled
environment.
4.6 The project foundation engineer, architect, and/or developer should determine the thickness
of bedding sand below the slab. In general, 3 to 4 inches of sand bedding is typically used.
Geocon should be contacted to provide recommendations if the bedding sand is thicker
than 6 inches.
4.7 The foundation design engineer should provide appropriate concrete mix design criteria and
curing measures to assure proper curing of the slab by reducing the potential for rapid
moisture loss and subsequent cracking and/or slab curl. The foundation design engineer
should specify the concrete mix design and proper curing methods on the foundation plan. It
is critical that the foundation contractor understands and follows the recommendations
presented on the foundation plan.
4.8 As an alternative to the conventional foundation recommendations, consideration should be
given to the use of post-tensioned concrete slab and foundation systems for the support of the
proposed structures. The 2013 CBC has updated the design requirements for post-tensioned
foundation systems. The post-tensioned systems should be designed by a structural engineer
experienced in post-tensioned slab design and design criteria of the Post-Tensioning Institute
(PT!), Third Edition, as required by the 2013 CBC (Section 1805.8). Although this procedure
was developed for expansive soil conditions, we understand it can also be used to reduce the
potential fOr foundation distress due to differential fill settlement. The post-tensioned design
should incorporate the geotechnical parameters presented in Table 4.3 for the particular
Foundation Category designated. The parameters presented in Table 4.3 are based on the
guidelines presented in the PTI, Third Edition design manual.
Project No. 07135-42-05 _10- October 10, 2016
TABLE 4.3
POST-TENSIONED FOUNDATION SYSTEM DESIGN PARAMETERS
Post-Tensioning Institute (PT!)
Third Edition Design Parameters
Foundation Category
III
Thornthwaite Index -20 -20 -20
Equilibrium Suction 3.9 3.9 3.9
Edge Lift Moisture Variation Distance, em (feet) 5.3 5.1 4.9
Edge Lift, YM (inches) 0.61 1.10 1.58
Center Lift Moisture Variation Distance, em (feet) 9.0 9.0 9.0
Center Lift, YM (inches) 0.30 0.47 0.66
4.9 If the structural engineer proposes a post-tensioned foundation design method other than
the 2013 CBC:
The criteria presented in Table 4.3 are still applicable.
Interior stiffener beams should be used for Foundation Categories II and III.
The width of the perimeter foundations should be at least 12 inches.
The perimeter footing embedment depths should be at least 12 inches, 18 inches
and 24 inches for foundation categories I, II, and III, respectively. The embedment
depths should be measured from the lowest adjacent pad grade.
4.10 The foundations for the post-tensioned slabs should be embedded in accordance with the
recommendations of the structural engineer. If a post-tensioned mat foundation system is
planned, the slab should possess a thickened edge with a minimum width of 12 inches and
extend at least 6 inches below the clean sand or crushed rock layer.
4.11 Our experience indicates post-tensioned slabs are susceptible to excessive edge lift,
regardless of the underlying soil conditions. Placing reinforcing steel at the bottom of the
perimeter footings and the interior stiffener beams may mitigate this potential. Current PTI
design procedures primarily address the potential center lift of slabs but, because of the
placement of the reinforcing tendons in the top of the slab, the resulting eccentricity after
tensioning reduces the ability of the system to mitigate edge lift. The structural engineer
should design the foundation system to reduce the potential of edge lift occurring for the
proposed structures.
4.12, During the construction of the post-tension foundation system, the concrete should be
placed monolithically. Under no circumstances should cold joints form between the
Project No. 07135-42-05 - 11 - October 10, 2016
footings/grade beams and the slab during the construction of the post-tension foundation
system.
4.13 Category I, II, or III foundations may be designed for an allowable soil bearing pressure of
2,000 pounds per square foot (psf) (dead plus live load). This bearing pressure may be
increased by one-third for transient loads due to wind or seismic forces. The estimated
maximum total and differential settlement for the planned structures due to foundation
loads is I- inch and '/2-inch, respectively. Differential settlement is estimated to occur over
a span of 40 feet.
4.14 Isolated footings, including PT foundation systems where footings are not reinforced with
PT cables, should have the minimum embedment depth and width recommended for
conventional foundations (see Section 4.1 through 4.3) for a particular foundation category.
The use of isolated footings, which are located beyond the perimeter of the building and
support structural elements connected to the building, are not recommended for Category
III. Where this condition cannot be avoided, the isolated footings should be connected to
the building foundation system with grade beams.
4.15 For Foundation Category III, consideration should be given to using interior stiffening
beams and connecting isolated footings and/or increasing the slab thickness. In addition,
consideration should be given to connecting patio slabs, which exceed five feet in width, to
the building foundation to reduce the potential for future separation to occur.
4.16 Special subgrade presaturation is not deemed necessary prior to placing concrete; however,
the exposed foundation- and slab-subgrade soil should be moisture conditioned, as necessary,
to maintain a moist condition as would be appropriate in any such concrete placement.
4.17 Where buildings or other improvements are planned near the top of a slope steeper than 3:1
(horizontal:vertical), special foundations and/or design considerations are recommended
due to the tendency for lateral soil movement to occur.
For fill slopes less than 20 feet high or cut slopes regardless of height, footings
should be deepened such that the bottom outside edge of the footing is at
least 7 feet horizontally from the face of the slope. r.
For fill slopes greater than 20 feet high, foundations should be extended to a depth
where the minimum horizontal distance is equal to H13 (where H equals the
vertical distance from the top of the fill slope to the base • of the fill soil) with a
minimum of 7 feet but need not exceed 40 feet. The horizontal distance is
measured from the outer, deepest edge of the footing to the face of the slope. A
post-tensioned slab and foundation system or mat foundation system can be used to
Project No. 07135-42-05 -12 - - October 10, 2016
help reduce potential foundation distress associated with slope creep and lateral fill
extension. Specific design parameters or recommendations for either of these
alternatives can be provided once the building location and fill slope geometry
have been determined.
If swimming pools are planned, Geocon Incorporated should be contacted for a
review of specific site conditions.
Swimming pools located within 7 feet of the top of 'cut or fill slopes are not
recommended. Where such a condition cannot be avoided, the portion of the
swimming pool wall within 7 feet of the slope face be designed assuming that the
adjacent soil provides no lateral support. This recommendation applies to fill
slopes up to 30 feet in height, and cut slopes regardless of height. For swimming
pools located near the top of fill slopes greater than 30 feet in height, additional
recommendations may be required and Geocon Incorporated should be contacted
for a review of specific site conditions.-
Although other improvements that are relatively rigid or brittle, such as concrete
flatwork or masonry walls, may experience some distress if located near the top of
a slope, it is generally not economical to mitigate this potential. It may be possible,
however, to incorporate design measures that would permit some lateral soil
movement without causing extensive distress. Geocon Incorporated should be
consulted for specific recommendations.
4.18 The exterior flatwork recommendations provided herein assumes that the near surface soils
are very low to medium (El < 90). Exterior slabs not subjected to vehicular traffic should
be a minimum of four inches thick and reinforced with 6 x 6-6/6 welded wire mesh. The
mesh should be placed in the middle of the slab. Proper mesh positioning is critical to
future performance of the slabs. The contractor should take extra measures to provide
proper mesh placement. Prior to construction of slabs, the upper 12 inches of subgrade soils
should be moisture conditioned at or slightly above optimum moisture content and
compacted to at least 90 percent of the laboratory maximum dry density per ASTM 1557.
4.19 The recommendations of this report are intended to reduce the potential for cracking of
slabs due to expansive soil (if present), differential settlement of existing soil or soil with
varying thicknesses. However, even with the incorporation of the recommendations
presented herein, foundations, stucco walls, and slabs-on-grade placed on such conditions
may still exhibit some cracking due to soil movement and/or shrinkage. The occurrence of
concrete shrinkage cracks is independent of the supporting soil characteristics. The
occurrence may be reduced and/or controlled by: (1) limiting the slump of the concrete,
(2) proper concrete placement and curing, and by (3) the placement of crack control joints
at periodic intervals, in particular, where re-entrant slab corners occur.
Project No. 07135-42-05 - 13 - October 10, 2016
4.20 Geocon Incorporated should be consulted to provide additional design parameters as
required by the structural engineer.
5.0 Retaining Walls and Lateral Loads
5.1 Retaining walls not restrained at the top and having a level backfill surface should be
designed for an active soil pressure equivalent to the pressure exerted by a fluid density of
35 pcf. Where the backfill will be inclined at 2:1 (horizontal:vertical), an active soil
pressure of 50 pcf is recommended. These soil pressures assume that the backfill materials
within an area bounded by the wall and a 1:1 plane extending upward from the base of the
wall possess an Expansion Index of 50 or less. Expansive soil should not be used as
backfill material behind retaining walls.
5.2 Where walls are restrained from movement at the top, an additional uniform pressure of
8H psf (where H equals the height of the retaining wall portion of the wall in feet) should
be added to the active soil pressure where the wall possesses a height of 8 feet or less and
12H where the wall is greater than 8 feet. For retaining walls subject to vehicular loads
within a horizontal distance equal to two-thirds the wall height, a surcharge equivalent to
two feet of fill soil should be added (soil total unit weight 130 pcf).
5.3 Soil to be used as backfill should be stockpiled and samples obtained for laboratory testing
to evaluate its suitability for use as wall backfill. Modified lateral earth pressures will be
required if backfill soils do not meet the required expansion index. Standard wall designs,
if used, are based on a specific active lateral earth pressure and/or soil friction angle. On-
site soils might not meet the design values used for the standard wall design. Geocon
Incorporated should be consulted if standard wall designs will be used to assess the
suitability of on-site soil for use as wall backfill.
5.4 Unrestrained walls will move laterally when backfilled and loading is applied. The amount
of lateral deflection is dependent on the wall height, the type of soil used for backfill, and
loads acting on the wall. The wall designer should provide appropriate lateral deflection
quantities for planned retaining walls structures, if applicable. These lateral values should
be considered when planning types of improvements above retaining wall structures.
5.5 Retaining walls should be provided with a drainage system adequate to prevent the buildup
of hydrostatic forces and should be waterproofed as required by the project architect. The
use of drainage openings through the base of the wall (weep holes) is not recommended
where the seepage could be a nuisance or otherwise adversely affect the property adjacent
to the base of the wall. The above recommendations assume a properly compacted granular
Project No. 07135-42-05 -14 - October 10, 2016
(El 50) free-draining backfill material with no hydrostatic forces or imposed surcharge
load. A typical retaining wall drainage detail is presented on Figure 4. If conditions
different than those described are expected, or if specific drainage details are desired,
Geocon Incorporated should be contacted for additional recommendations.
5.6 / In general, wall foundations having a minimum depth and width of .1 foot may be designed
for an allowable soil bearing pressure of 2,000 psf, provided the soil within 3 feet below
the base of the wall has an Expansion Index < 90. The recommended allowable soil bearing
pressures may be increased by 300 psf and 500 psf for each additional foot of foundation
width and depth, respectively, up to a maximum allowable soil bearing pressure of
4,000 psf. The proximity of the foundation to the top of a slope steeper than 3:1 could
impact the allowable soil bearing pressure. Therefore, Geocon Incorporated should be
consulted where such a condition is expected.
5.7 The structural engineer should determine the seismic design category for the project in
accordance with Section 1613 of the CBC. If the project possesses a seismic design
category of D, E, or F, retaining walls that support more than 6 feet of backfill should be
designed with seismic lateral pressure in accordance with Section 18.3.5.12 of the 2013
CBC. The seismic load is dependent on the retained height where H is the height of the
wall, in feet, and the calculated loads result in pounds per square foot (psf) exerted at the
base of the wall and zero at the top of the wall. A seismic load of 21H should be used for
design. We used the peak ground acceleration adjusted for Site Class effects, PGAM, of
0.445 g calculated from ASCE 7-10 Section 11.8.3 and applied a pseudo-static coefficient
of 0.33.
5.8 For resistance to lateral loads, an allowable passive earth pressure equivalent to a fluid
density of 300 pcf is recommended for footings or shear keys poured neat against properly
compacted granular fill soils or undisturbed formation materials. The allowable passive
pressure assumes a horizontal surface extending away from the base of the wall at least
5 feet or three times the surface generating the passive pressure, whichever is greater. The
upper 12 inches of material not protected by floor slabs or pavement should not be included
in the design for lateral resistance. Where walls are planned adjacent to and/or on
descending slopes, a passive pressure of 150 pcf should be used in design.
5.9 An allowable friction coefficient of 0.35 may be used for resistance to sliding between soil
and concrete. This friction coefficient may be combined with the allowable passive earth
pressure when determining resistance to lateral loads.
Project No. 07135-42-05 - 15 - October 10, 2016
5.10 The recommendations presented above are generally applicable to the design of rigid
concrete or masonry retaining walls having a maximum height of eight feet. In the event
that walls higher than eight feet or other types of walls (i.e., soil nail, MSE walls) are
planned, Geocon Incorporated should be consulted for additional recommendations.
6.0 Slope Maintenance
6.1 Slopes that are steeper than 3:1 (horizontal:vertical), under conditions that are both difficult
to prevent and predict, may be susceptible to near-surface slope instability. The instability
is typically limited to the outer 3 feet of a portion of the slope and usually does not directly
impact the improvements on the pad areas above or below the slope. The occurrence of
surficial instability is more prevalent on fill slopes and is generally preceded by a period of
heavy rainfall, excessive irrigation, or the migration of subsurface seepage. The disturbance
and/or loosening of the surficial soils, as might result from root growth, soil expansion, or
excavation for irrigation lines and slope planting, may also be a significant contributing
factor to surficial instability. It is therefore recommended that, to the maximum extent
practical: (a) disturbed/loosened surficial soils either be removed or properly
recompacted, (b) irrigation systems be periodically inspected and maintained to eliminate
leaks and excessive irrigation, and (c) surface drains on and adjacent to slopes be
periodically maintained to preclude ponding or erosion. It should be noted that although the
incorporation of the above recommendations should reduce the potential for surficial slope
instability, it will not eliminate the possibility, and, therefore, it may be necessary to
rebuild or repair a portion of the project's slopes in the future.
7.0 Detention Basin and Bioswale Recommendations
7.1 Any permanent detention basins, bioswales, and bio-remediation areas should be designed
by the project civil engineer and reviewed by Geocon Incorporated. Typically, bioswales
consist of a surface layer of vegetation underlain by clean sand. A subdrain should be
provided beneath the sand layer. Prior to discharging into the storm drain pipe, a seepage
cutoff wall should be constructed at the interface between the subdrain and storm drainpipe.
The concrete cut-off wall should extend at least 6-inches beyond the perimeter of the
gravel-packed subdrain system.
7.2 Distress may be caused to planned improvements and properties located hydrologically
downstream or adjacent to these devices. The distress depends on the amount of water to be
detained, its residence time, soil permeability, and other factors. We have not performed a
hydrogeology study at the site. Downstream and adjacent properties may be subjected to
seeps, springs, slope instability, raised groundwater, movement of foundations and slabs, or
other impacts as a result of water infiltration. Due to site soil and geologic conditions,
Project No. 0713542-05 -16 - October 10, 2016
permanent bioswales and bio-remediation areas should be lined with an impermeable
barrier, such as a thick visqueen, to prevent water infiltration in to the underlying
compacted fill. Temporary detention basins in areas where improvements have not been
constructed do not need to be lined.
7.3 The landscape architect should be consulted to provide the appropriate plant
recommendations. If drought resistant plants are not used, irrigation may be required.
8.0 Site Drainage and Moisture Protection
8.1 Adequate site drainage is critical to reduce the potential for differential soil movement,
erosion and subsurface seepage. Under no circumstances should water be allowed to pond
adjacent to footings. The site should be graded and maintained such that surface drainage is
directed away from structures in accordance with 2013 CBC 1803.3 or other applicable
standards. In addition, surface drainage should be directed away from the top of slopes into
swales or other controlled drainage devices. Roof and pavement drainage should be
directed into conduits that carry runoff away from the proposed structure.
8.2 In the case of basement walls or building walls retaining landscaping areas, a water-
proofing system should be used on the wall and joints, and a Miradrain drainage panel (or
similar) should be placed over the waterproofing. The project architect or, civil engineer
should provide detailed specifications on the plans for all waterproofing and drainage.
8.3 Underground utilities should be leak free. Utility and irrigation lines should be checked
periodically for leaks, and detected leaks should be repaired promptly Detrimental soil
movement could occur if water is allowed to infiltrate the soil for prolonged periods of
time.
8.4 Landscaping planters adjacent to paved areas are not recommended due to the potential for
surface or irrigation water to infiltrate the pavement's subgrade and base course. We
recommend the use of drains to collect excess irrigation water and'transmit it to drainage
structures, or impervious above-grade planter boxes. In addition, where landscaping is
planned adjacent to the pavement, we recommend construction of a cutoff wall along the
edge of the pavement that extends at least six inches below the bottom of the base material.
LIMITATIONS
The conclusions and recommendations contained herein apply only to our work with respect to
grading, and represent conditions at the date of final observation on September 29, 2016. Any
subsequent grading should be done in conjunction with our observation and testing services. As used
Project No. 07135-42-05 -17- October 10, 2016
herein, the term "observation" implies only that we observed the progress of the work with which we
agreed to be involved. Our services did not include the evaluation or identification of the potential
presence of hazardous or corrosive materials. Our conclusions and opinions as to whether the work
essentially complies with the job specifications are based on our observations, experience and test
results. Subsurface conditions, and the accuracy of tests used to measure such conditions, can vary
greatly at any time. We make no warranty, expressed or implied, except that our services were
performed in accordance with engineering principles generally accepted at this time and location.
We will accept no responsibility for any subsequent changes made to the site by others, by the
uncontrolled action of water, or by the failure of others to properly repair damages caused by the
uncontrolled action of water. It is the responsibility of owner to ensure that the information and
recommendations contained herein are brought to the attention of the architect and engineer for the
project, are incorporated into the plans, and that the necessary steps are taken to see that the
contractor and subcontractors carry out such recommendations in the field. Recommendations that
pertain to the future maintenance and care for the property should be brought to the attention of future
owners of the property or portions thereof. The findings and recommendations of this report may be
invalidated wholly or partially by changes outside our control. Therefore, this repoit is subject to
review and should not be relied upon after a period of three years.
Should you have any questions regarding this report, or if we may be of further service, please
contact the undersigned at your convenience.
Very truly yours,
GEOCON INCORPORATED
ALI
CEG 1778 CERTIFIED GE 2533 ENGINEERING
(P GEOLOGIST
AS:RCM:dmc
PC
(1) Addressee
(3) Cornerstone Communities
Attention: Mr. Bob Seaman
Project No. 07135-42-05 -18- October 10, 2016
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WALL / COLUMN FOOTING DIMENSION DETAIL
GEOCON
INCORPORATED (low),
GEOTECHNICAL. ENVIRONMENTAL. MATERIALS
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121- 2974
PHONE 858 558-6900 - FAX 858 558-6159
RM I AML DSK/GTYPD
QUARRY CREEK R-4 EAST
LOTS 20 AND 21
CARLSBAD, CALIFORNIA
DATE 10-10-2016 1 PROJECT NO. 07135 - 42 - 05 FIG.3
Plotteth110110l2016 1:07PM I By.ALVIN LADRILLONO I File Loeeticey.'.PROJECTS107135-42.05 (Quarry Creek. R4)IDETAILS1Wo0.Colunrn Fookeg Oiererreee DReg (COI.FOOT2).dwg
CONCRETE j— GROUND SURFACE PROPOSED BROWDITCH
RETAINING WALL
I
PROPERLY-' - ED
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PER ARCHITECT
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2/3 H . MIRAFI 140N FILTER FABRIC
(OR EQUIVALENT)
: ,-_OPEN GRADED
- 1" MAX AGGREGATE
GROUND SURFACE
FOOTING 4" DIA. PERFORATED SCHEDULE
77,757- R- 40 PVC PIPE EXTENDED TO
APPROVED OUTLET
12"
I PROPOSED
CONCRETE
BROWDITCH
RETAINING
WALL -
2/3 H
GROUND SURFACE CONCRETE i—GROUND SURFACE BROWDITCH
RETAINING -
WALL -
WATER PROOFING
__— PER ARCHITECT
2/3H DRAINAGE PANEL
(MIRADRAIN 6000
OR EQUIVALENT)
- 4" DIA. SCHEDULE 40
'- PERFORATED PVC PIPE
()) OR TOTAL DRAIN
EXTENDED TO
APPROVED OUTLET
NO SCALE
GEOCON
INCORPORATED
GEOTECHNICALu ENVIRONMENTAL • MATERIALS
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121- 2974
PHONE 858 558-6900 - FAX 858 558-6159
RM / AML DSK/GTYPD
QUARRY CREEK R-4 EAST
LOTS 20 AND 21
CARLSBAD, CALIFORNIA
DATE 10-10-2016 PROJECT NO. 07135 - 42 - 05 FIG.4
Plotted 10/10/2016 1:07PM I By-ALVIN LADRILLONO I File L000tko:Y:/PROJECTS/07135-42.05 (0000y C,eek - R4)0ETAILS/Typ1ot1 Re legWofl D,aieoge Debt IRWDD7AIdwg
TABLE I
GEOCON SUMMARY OF FIELD DENSITY TEST RESULTS
Project Name Quarry Creek Project No.: 07135-42-05
Elev. Max. Opt. Field Field Required Relative Test No. or Curve Dry Moist Dry Moisture Relative Date Location Rock Content. Content Compaction Depth No. Density Density Compaction
( o) (feet)
Re.
(pci) (%) (pci) (%) (%)
Pre. No.
501 10/06/15 R-4 E Lot 20 128.0 14 0 124.6 11.3 115.4 11.6 93 90
502 10/06/15 R-4E Lot 21 127.0 14 0 124.6 11.3 113.3 10.9 91 90
FG 537 10/16/15 R-4E Lot 20 . 129.1 14 0 124.6 11.3 117.1 11.3 94 90
FG 538 10/16/15 R-4E Lot 21 128.4 14 0 124.6 11.3 112.6 10.9 90 90
FG 830 09/29/16 Lot 20 0.0 14 0 124.6 11.3 118.4 11.7 95 90
FG 831 09/29/16 Lot 21 0.0 14 0 124.6 11.3 120.2 12.1 96 90
..........................................j
TABLE 1 GEO:CON EXPLANATION OF CODED TERMS
TEST NO. PREFIX
AC Asphalt Concrete IT Irrigation Trench SL Sewer Lateral
AD Area Drain iT Joint Trench SM Sewer Main
B Base M Moisture Test SR Slope Repair
CG Curb/Gutter MSE Mechanically Stabilized Earth Wall ST Slope Test
DW Driveway RG Regrade SW Sidewalk
ET Electrical Trench RWL Reclaimed Water Lateral SZ Slope Zone
ETB Exploratory Trench RWM Reclaimed Water Main UT Utility Trench
FB Footing Backfill SBT Subdrain Trench WB Wall Backfill
FG Finish Grade SD Storm Drain WL Water Lateral
GT Gas Trench SG Subgrade WM Water Main
TEST NO. RE.
A, B, C, ... Retest of previous density test failure following additional moisture conditioning or recompaction
R Fill in area of density test was removed during construction operations
ELEVATION OR DEPTH
Cooresponds to the elevation or the depth, in feet, of the in-place density/moisture content test. The value has been rounded to the
nearest whole foot
CURVE NO.
Corresponds to the curve numbers presented in the summary of the laboratory maximum dry density and optimum moisture content test
resluts. The field representative selected the curve no. based on the laboratory test results and field observations
>%" ROCK - ROCK CORRECTION
The laboratory maximum dry density and optimum moisture content can be adjusted for in-place soil that possesses rock larger than %
inch. The curve no. is adjusted for the percentage of % inch rock in accordacne with ASTM D 4718 or Woodward Clyde guidelines. ................•.•....•..•.•....•.......... I
TABLE II
SUMMARY OF LABORATORY MAXIMUM DRY DENSITY AND
OPTIMUM MOISTURE CONTENT TEST RESULTS
ASTM D 1557
Sample
No. Description
Maximum
Dry Density
(Pei)
Optimum
Moisture Content
(% dry weight)
5 Dark brown, Clayey, fine SAND 130.9 8.9
8 Olive brown, Sandy GRAVEL 135.0 7.6
9 Light greenish brown, Clayey, fine to coarse SAND 125.2 11.1
12 Reddish brown, Clayey, fine to coarse SAND, with GRAVEL 13.08 9.5
13 Light greenish brown, Silty, Sandy CLAY, some gravel 118.1 13.3
14 1 Light gray, Silty, fine to coarse SAND, with gravel 124.6 11.3
15 Light brown, Silty, fine to coarse SAND 128.1 10.2
17 Very dark brown to black Sandy CLAY 112.7 15.5
TABLE III
SUMMARY OF LABORATORY EXPANSION INDEX TEST RESULTS
ASTM D 4829
Moisture Content (%) Dry Expansion ASTM
I No. Representative Lot . p Density Index Classification Before Test I After Test (pci) (per 2013 CBC)
EI-19 20 through 23 9.6 17.4 1 111.9 32 Low
TABLE IV
SUMMARY OF LABORATORY WATER-SOLUBLE SULFATE TEST RESULTS
CALIFORNIA TEST NO. 417
Sample No. Representative Lot Water-Soluble Sulfate (%) Sulfate Exposure
EI-19 20 through 23 0.014 Not Applicable (SO)
Project No. 07135-42-05 October 10, 2016
Lot No. Pad Condition
Approximate
Maximum Depth
Approximate
Depth of Fill Expansion Recommended
of Fill (feet) Differential (feet) Index Foundation Category
20 Undercut due to 4 1 32 I Expansive Soil
21 Undercut due to 4 1 32 I Expansive Soil
TABLE
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND RECOMMENDED FOUNDATION CATEGORY FOR
QUARRY CREEK, R-3 AND R-8
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S
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S
S
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Project No. 07135-42-05 October 10, 2016